What's the point of prime minister's questions?

So, what is the point of prime minister's questions? I was going to respond yesterday to the various people who asked yesterday why we should bother live-blogging it, but - to be honest - it's taken me a while to come up with some decent answers.

Apart from "pointless" (which we'll get on to in a moment), I thought Trouserpress was pretty much spot on. Others agreed too, and I was really struck by musttryharder, who despaired at getting any answers from the PM and concluded: "All I get is frustration and annoyance with self for bothering to show an interest."

It's the obvious answer and badman gave it yesterday. Being "accountable" is important in democratic politics. It means that, if anyone exercises power in our name, they have to be able to say what they've done and why they've done it. It makes for good governance (because knowing that they will be held to account encourages politicians to perform more effectively). And watching the scoundrels squirms sometimes makes the voters feel good too.

Of course, the theory breaks down if the PM doesn't answer the question - if he doesn't say what he's done and why he's done it. But accountability doesn't fail completely. As musttryharder said: "I suppose we can make a judgment on the man by the fact he does not answer the question."

2. It's a good way of finding out which political arguments work and which ones don't

PMQs isn't a Socratic dialogue. But Brown and David Cameron do engage in some kind of debate, and, if you listen, you can tell what lines of attack are effective and what ones aren't. For example, earlier this year it became obvious that Cameron couldn't say what he would do about Northern Rock. And it's clear that Brown can't defend the proposed backdated VED increase on green grounds.

The political parties finetune their campaign themes all the time and PMQs is one of the places where they do it. Next time you're listening and it seems boring, imagine that you are sitting in on a private strategy meeting for the general election, and it will suddenly seem a bit more interesting.

3. Leaders are sometimes defined by PMQs

It's true: Brown, Cameron and Nick Clegg spend the session throwing rhetorical mud at each other. But occasionally, if an insult has particular force - because of the truth it contains, and the verve with which it's expressed - it sticks. In fact, it can stick enough to change the way a politician is perceived. The jibes about Brown being a "ditherer" achieved this (to the extend that, a few weeks ago, I even heard a Today programme presenter talking about Brown "dithering", as if that was now objective fact).

Two better examples are Tony Blair's retort to John Major: "I lead my party, he follows his," and Vincent Cable's "From Stalin to Mr Bean" description of Brown. If these comments had been issued on paper, as a press release, they would have been forgotten. But, deployed in the cockpit of PMQs, they grabbed the public imagination, causing huge damage to the images of Major and Brown.

4. PMQs affects the way leaders are perceived by the public - a bit

There's an argument to be had about how much influence the way a leader is perceived has on a party's fortunes. But it must count for a bit. And PMQs must have an effect on the way the public view Brown, Cameron and Clegg.

5. PMQs affects the way leaders are perceived by their MPs - a lot

Outside the Westminster village, it might not count for much. But inside the village, it matters hugely. One of the reasons William Hague lasted four years as party leader, when the Tories were performing abysmally at the national level, was because he was brilliant at PMQs. But Iain Duncan Smith was feeble at the dispatch box, which was partly why his MPs decided he had to go.

6. Sometimes you do get an answer

Admittedly, not often. Brown's stock response to most questions (when he's not engaged in partisan banter with Cameron) is: (a) x is an important issue, (b) the government has already done this, this and this about x, and (c) we want to do a bit more. But sometimes we do learn something. Remember the surprise when Brown was asked about supercasinos or the reclassification of cannabis and he told us the government's policy was going to change.

7. And it can be fun

Of course it can be awful. But sometimes it's good. Hague has been off-form recently, but as Tory leader he was superb. And, even though the Cameron/Brown insults are pretty low-grade, sometimes they can make you smile.

So, I think it's worth it. We'll be back blogging it again in October.